Adverse childhood experiences (ACE) are potentially important and modifiable social determinants of adolescent HIV risk. While the relationship between ACE and sexual health has been documented in the US other high-income contexts with concentrated epidemics, evidence from lower-income high-HIV prevalence contexts is largely missing. Moreover, no study has considered how adversities cluster and compound across the life course, interact across ecological levels, and contribute to a common causal chain culminating in HIV infection. The proposed project will create an adolescent cohort that has been traced since birth by building on exceptional existing data provided by parents in the Malawi Longitudinal Study of Families and Health (MLSFH; established in 1998). We propose collecting two new rounds of prospective data directly from the MLSFH children as they reach adolescence; in doing so, we will establish a cohort that is currently entering a critical age-range for HIV risk as they transition to adulthood. The aims are: Aim 1. To describe the prevalence, co-occurrence and re-occurrence of Adverse Childhood Experiences among adolescents in a HIV-endemic low-income country. We will construct indicators of ACE covering the period from infancy to adolescence by linking 1) rich data captured through parental reporting in prior MLSFH waves and 2) new data collected from adolescents (at age 11-15 and at 14-18) using the Adverse Childhood Experiences ? International Questionnaire (ACE-IQ) recently developed by the WHO. Aim 2. To estimate the causal impact of ACE on the emergence of differentiated HIV risk trajectories during adolescence. By applying sophisticated statistical methods, we will be able to examine the causal role of early and ongoing adversities on the emergence of HIV risk, including 1) poor transitions to adulthood 2) behavioral risk and 3) HIV and HSV2 incidence. Aim 3. To highlight potential intervention points by identifying causal mediators between ACE and HIV risk. We focus on social, emotional, and cognitive impairments that may result from frequent or chronic activation of the stress response and may also contribute to social or behavioral HIV risk. Aim 4: To identify protective factors that moderate the impact of ACE on HIV risk. We will test potential multi-level sources of resilience (e.g., family resources, peer support, government programs) that may determine how children cope could be enhanced through intervention. A rigorous evaluation of the consequences, mediators, and moderators of childhood adversity on adolescent HIV risk will greatly enhance current HIV prevention strategies in low income countries by explaining why some adolescents engage in high risk behaviors and contract HIV while others do not, and by identifying modifiable targets for intervention. By integrating the project into an ongoing longitudinal study, we rapidly create a birth cohort, facilitate causal inference, ensure timely findings, and add value to an existing, widely-used resource for research on HIV and health in sub-Saharan Africa.